The entire eastern part of Porquerolles island, including Cap des Mèdes, is made up of phyllades of Hyères. They consist of epizonal metamorphic rocks of the superficial zone of the earth's crust where metamorphism has occurred at moderate temperature. These phyllades of Hyères form the western and eastern halves of the Medes peninsula, while the highest promontory of the Medes, oriented north-south, consists of quartzite phyllades.